Other Environmental Stresses at Altitude

Individuals at high altitude are subjected to low temperature, wind, and ultraviolet radiation. The effects of hypoxia may therefore be compounded by hypothermia, dehydration, frostbite, and sunburn. On the basis of a seemingly higher incidence of stroke,^[263] thrombophlebitis, and pulmonary thromboembolism^[264] at high altitude, it has been suspected that prolonged hypoxic exposure may cause hypercoagulability. Indeed, rapid exposure to altitude in a hypobaric chamber has been associated with a decrease in partial thromboplastin time,^[265] an increase in prothrombin fragments 1 and 2, and an increase in thrombin-antithrombin complex and factor VIIa activity.^[266] However, gradual exposure to altitude has not been linked to measurable changes in either coagulation or fibrinolysis under resting conditions.^[267]